1. Field of the Invention
The present invention relates to a technique for preventing clipping of an audio signal.
2. Description of the Related Art
In order to output an audio signal via a speaker or headphones (which will collectively be referred to as a “speaker” hereafter), an amplifier circuit configured to amplify an infinitesimal electrical signal is employed. The level of the audio signal to be input to the amplifier circuit, i.e., the volume, changes over time in increments of input sources according to the audio content to be reproduced, or according to the state of an upstream circuit. For example, while viewing television, it is well known that there is a significant difference in volume between television programs and commercials. With an arrangement employing an amplifier circuit having a constant gain, in a case in which the audio signal is overly loud, it exceeds the possible range of amplification in a downstream stage, which results in the signal being clipped (clamped), and distortion occurs.
In order to solve such a problem, a method is employed in which the audio signal level is monitored, and the gain of a variable gain amplifier circuit is controlled. In general, such a method is also referred to as AGC (Automatic Gain Control).